The present invention relates to a warming structure of a gas turbine rotor, and particularly, more to a rotor warming structure which is so improved as to be suited for reducing a thermal stress generated in the inner peripheral part of a disk when a gas turbine is started.
An example of flow of air extracted from a compressor to cool a turbine blade in a gas turbine rotor of a conventional type is disclosed in Japanese Patent Laid-Open No. 22003/1985. The gas turbine rotor disclosed therein comprises a first stage disk, a second stage disk, a spacer disposed between the first and second stage disks, and front and rear side shafts sandwiching therebetween the first and second stage disks and the spacer and joined thereto. The first and second disks each have a central hole. The rotor has a construction that the air extracted from the compressor is introduced into first and second stage blades mounted on the first and second disks, respectively, through a central hole of the front side shaft, the central holes of the first and second disks and a space between the first and second disks in order to cool the blades.
In this rotor structure, the extracted compressor air does not flow to the central hole of the second stage disc because the central hole of the second stage disc and a central hole of the rear side shaft form a blind air passage.
The temperature of the blades rises when a gas turbine is started, since they are exposed to a high-temperature gas. The temperature of the outer peripheral part of a turbine disk rises in a short time due to the heat conduction from the blade. Meanwhile, the inner peripheral part of the disk is heated by the extracted compressor air having a temperature of about 350.degree. C., in the case of the first-stage disk, so that temperture thereof rises. However, the speed of the rise of the temperature is much slower on the inner peripheral side than on the outer peripheral side. This causes a large temperature difference between the inner and outer peripheries of the disk in the course of the starting, and a high thermal stress on the tensile side is generated in the inner peripheral part of the disk by this temperature difference. Simultaneously, a centrifugal stress is generated in the disk due to rotation of the rotor, and the superposition of said thermal stress and the centrifugal stress causes a very large stress in the inner peripheral part of the disk at the time of starting. While the inner surface of the central hole of the first-stage disk has a relatively high heat transfer coefficient (about 400 Kcal/m.sup.2 h.degree.C.) due to the flow speed of the extracted compressor air flowing through the central hole thereof as described above, the central hole of the second-stage disk has a still lower heat transfer coefficient about 100 Kcal/m.sup.2 h.degree.C. since the extracted compressor air does not pass therethrough, and thus the disk has a structure which is hard to heat at the time of starting and which generates consequently a still higher thermal stress than the first-stage disk.
Although a turbine rotor is so designed, in a conventional gas turbine, that a stress is held down to a level at which the turbine disk is prevented from breaking down even in the state of superposition of the thermal stress and the centrifugal stress at the time of the above-mentioned starting, the peripheral speed of the turbine is further increased as the performance of the turbine becomes high, and this has brought forth a problem that the stress generated in the disk due to the superposition of the centrifugal stress and the thermal stress becomes too high in the conventional structure of the rotor.
The problem of above-described prior art is that the stress generated in the disk, which is brought forth by the thermal stress generated at the time of starting being added to the centrifugal stress of the turbine disk, becomes too high when the peripheral speed of the gas turbine is further increased.
An example of a rotor warming structure of a combined turbine plant of a gas turbine and a steam turbine is disclosed in Japanese Patent Laid-Open No. 96102/1983, wherein a central gas passage is provided in gas turbine disks, front and rear side shafts, and a compressor gas extracted from a compressor enters the central gas passage. A major portion of the compressor gas entering the central gas passage is introduced into the gas turbine blades through a radial passage branched from the central gas passage to cool the gas turbine blades. The remaining small portion of the compressor gas entering the central gas passages passes through the central gas passage and it is sent to a steam turbine rotor to warm the stream turbine rotor.
When the gas turbine rotor construction is applied to a gas turbine not combined with a steam turbine, turbine efficiency decreases because there is a small amount of the extracted compressor gas passing through the central gas passage out of the gas turbine without cooling the gas turbine blades. Therefore, this rotor construction is not applicable to a gas turbine not combined with a steam turbine without decreasing the turbine efficiency.